<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>背景样式</title>
    <link type="text/css" rel="stylesheet" href="style.css">
</head>
<body>
<table id="tb">
    <tr>
        <th>姓名</th>
        <th>年龄</th>
        <th>性别</th>
    </tr>
    <tr >
        <td>张三</td>
        <td>20</td>
        <td>男</td>
    </tr>
    <tr class="alt">
        <td>张三</td>
        <td>20</td>
        <td>男</td>
    </tr>
    <tr >
        <td>张三</td>
        <td>20</td>
        <td>男</td>
    </tr>
    <tr class="alt">
        <td>张三</td>
        <td>20</td>
        <td>男</td>
    </tr>
</table>
</body>
</html>